Artificial diamond is synthesized by a high pressure and high temperature (HPHT) method, a detonation method, or a chemical vapor deposition (CVD) method.
Diamond synthesized by the HPHT (synthesis conditions: about 50,000 air pressure and 1,400° C.) developed in 1955 has cubo-octahedron grit or irregular powder form with a size of below a few hundreds μm. Diamond obtained by a single crystal growth method performed also under the HPHT has a bulk form with a size of a few mm3. Diamond obtained by a detonation method (about 100,000 air pressure, 1,000° C.) has a powder form close to a spherical shape with a size of a few nm.
The general shape of diamond obtained by the HPHT method and the detonation method has such grit (or powder) form as natural diamond. This is because volume of an equipment that can generate a high pressure (above about 50,000 air pressure) to obtain diamond, a high temperature and high pressure phase of carbon, is limited.
Meanwhile, in 1980s, the CVD method (primary synthesizing conditions: about 100 Torr and 700° C.), by which diamond can be synthesized at below an atmospheric pressure, was developed so that more diverse types of diamond can be fabricated. According to the CVD synthesis method, a gas is activated by using heat or plasma in a certain vacuum container and deposited in a type of a polycrystalline film on a surface of a matrix(substrate) maintained at about 700° C. In this case, diamond is limited to be deposited on the surface of the matrix that contacts with vapor phase. In the CVD method, the synthesis area depends on volume of plasma generated in the used equipment, and the shape of diamond film depends on the shape of the used matrix. The diamond film is deposited with a thickness of a few nm˜a few mm on the platy matrix. It is used in the state of being attached on the matrix like an insert tool or a drill (direct coating: a thin film of below tens of μm) or used in a type of free standing film separated from the matrix(tens of μm˜a few mm). In addition, a diamond free standing film in a dome shape with a diameter of a few cm2 can be fabricated by using a matrix with a bent portion. In addition, by inducing a uniform nuclear generation in vapor phase according to the CVD method, a spherical diamond powder with a size of a few hundreds of nm can be synthesized.
However, the related art diamond synthesizing methods cannot fabricate diamond with a hollow shell structure.